Patent GB-1441928-A (GB)
Title: Peak detector
IPC: G04G99/00
Filed: 1972-12-18
Abstract: 1441928 Electronic watches RCA CORPORATION 15 June 1973 [18 Dec 1972] 58282/72 Heading G3T [Also in Divisions H2J and H3T] A circuit producing a pulse at signal peaks for pulsing the motor of a timepiece comprises an inverter having a negative feedback path operative during the peaks but otherwise normally inoperative. In the complementary inverter circuit shown the dimensions of the transistors P 1  and N 1  are so chosen that points B and C are almost at the supply potential V DD . A pulse train VA, Fig. 9 , such as may be derived from the balance wheel of a watch, causes the capacitor 16 to charge through diode 14 during the first slightly negative portion of the wave without much change in output voltage. During negative going portions of the wave the diode charges the capacitor to the peak value of the input signal so that positive going portions switch the state of the inverter and cut-off the diode. During the positive portion the capacitor discharges slightly so that during the next negative peak the condition of the circuit reverses again, as at 94, producing an output pulse, the width of which depends upon the amount of charge lost from capacitor C between the two positive pulses. To avoid missing a small peak following a large one the capacitor voltage may be limited by a diode to the supply voltage Fig. 12 (not shown). An inverter P2, N 2  provides the output wave VD. In order to charge the capacitor 16 more quickly where transistors P and N are small the diode 14 may be replaced by an emitter-follower transistor formed by lateral CMOS construction techniques, Fig. 5 (not shown). Alternatively a source follower may be used and driven from an extra amplifier stage the source to drain spurious diode formed on the substrate being rendered ineffective by following the source follower by an emitter follower Fig. 13  (not shown). In Figs. 18 and 19 (not shown) the feedback path is provided by the source drain path of a field effect transistor controlled by an amplifier connected to the output of the NOR gate. In addition the transistor may be connected in parallel with one of opposite conductive type controlled through an extra inverter Fig. 19 (not shown). Disabling of the circuit to prevent operation on undesired peaks may be effected by replacing the inverter by a complementary type NOR gate and controlling one of its inputs by an inhibit signal Fig. 7 (not shown). Alternatively a series gate formed by a pair of transistors in parallel may be connected in series with the base of the emitterfollower replacing diode 14, the parallel transistors being controlled by an inhibit signal Fig. 6 (not shown). A suitable NOR gate Fig. 8, comprises the main switching transistors P a  and Nb having their output peaks in series and transistors Pb and N a  connected in series and shunt respectively so that when an inhibit signal is applied at 42 the path through transistor P a  is broken and the path through Nb is short circuited. When the circuit is used to control the coil 71 Fig. 10 of a stepping motor of a watch, false operation may occur due to the intermediate peak in the voltage across the motor coil Fig. 11, when the back emf due to the movement of the motor becomes effective. In addition the drive pulse may be unnecessarily long (as shown by the dotted curve). Accordingly when a drive pulse occurs at 66 and the NOR gates switches on drive to transistor 62 an inhibit pulse is applied at 68. This pulse terminates at the end of the first dip and the peak detector circuit accordingly produces a "detect pulse", Fig. 11. This pulse ends when the motor coil voltage starts to go positive and reverses a bi-stable circuit 67 to switch off transmission providing coil drive. Accordingly the drive ends before the end of the motor drive pulse at 66. A suitable oscillator and frequency divider circuit for providing the motor drive and inhibit pulses are described with reference to Figs. 15 and 16 (not shown).